System for and method of controlling hysteresis motors



Feb. 19, 1952 H. c. ROTERS Q 2,586,095

SYSTEM FOR AND METHOD OF CONTROLLING HYSTERESIS MOTORS Filed April 25, 1949 FIG.|

lOd I70 I00 I00 lob lOd i ll CSO|EIRRAOLL CON'IPROL o SIGIEAL 23 FIG 3 F|G 4 ,4||Il|lll INVENTOR. HERBERT G. ROTERS ATTORNEY Patented Feb. 19, 1952 OFFICE SYSTEM FOR AND METHOD OF'CONTROL- LING HYSTERESIS MOTORS Herbert G. Roters, Kew Gardens, N. Y., assignor to Fairchild Camera and Instrument Corporation, a corporation of Delaware Application April 25, 1949, Serial No. 89,408

2 Claims. 1

. This invention relates to a system for and method of controlling hysteresis motors and, more particularly, to such a system and method for controlling and regulating the speed of such motors either during normal sub-synchronous operation or by braking upon de-energization.

Hysteresis motors have found rather widespread use in fractional horsepower and micropower sizes, particularly where synchronous operation is desired, since they constitute one of the most economical forms of low-power synchronous motors. Such motors have also found wide application in the control field because of their uniform sensitivity to control excitation in all angular positions.

It is well known that hysteresis motors, if not overloaded, are inherently synchronous in operation and, while such characteristic is usually used to advantage, it frequently becomes desirable to be able to control the speed of the motor, which implies a reduction of the motor speed below synchronism since super-synchronous speeds are not readily attainable. For example, in certain applications it is desirable rapidly to reduce the speed of such a motor to zero upon de-energization, that is, to brake the motor rapidly and uniformly to a standstill. Further, there are certain applications where hysteresis motors may be used to advantage, in which it is also desirable continuously to regulate or control the speed of the motor during normal operation at sub-synchronous speeds.

It is an object of the present invention, therefore, to provide a new and improved system for and method of controlling hysteresis motors by means of which the speed of the motor may be readily and uniformly reduced to zero for braking purposes.

It is another object of the invention to provide a new and improved system for and method of controlling hysteresis motors by means of which the speed of the motor may be continuously reguiated or controlled at sub-synchronous speeds.

In accordance with the invention, there is provided a motor control system comprising a synchronous hysteresis motor having a plurality of phase windings and a hysteresis rotor, a circuit for normally exciting the windings to develop a rotating magnetic field, and a control circuit for applying to at least one of the phase windings a current effective to develop a sub-synchronous magnetic field of a value to reduce the speed of the motor below synchronism. The motor control system also comprises impedance means for subatantially suppressing the flow of current in each z of the circuits of the frequency of the other of the circuits.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring now to the drawings, Fig. 1 is a schematic circuit diagram of a system for regulating or controlling the speed of a two-phase hysteresis synchronous motor; Fig. 2 is a schematic circuit diagram of a modification of the system of Fig. 1 embodying a split-phase singlephase motor which avoids the use of an auxiliary control winding; Fig. 3 is a schematic circuit diagram of a further modification of the system of Fig. 1 in which the speed of the hysteresis synchronous motor is automatically controlled in response to a control signal; Fig. 4 is a schematic circuit diagram of a simplified form of the system of Fig. 3; while Fig. 5 is a schematic circuit diagram of a system embodying a three-phase hysteresis synchronous motor and including an arrangement for automatically reducing the speed of the motor to zero in response to de-energization of the motor.

Referring now specifically to Fig. 1 of the drawings, there is represented a motor control system comprising a synchronous hysteresis motor In having a winding system including a pair of phase windings Illa and [0b and an auxiliary winding I00. The motor further includes a rotor llld of a material having a high hysteretic constant, such as a chrome steel or an aluminumnickel-cobalt alloy of the type commercially available as Alnico. The system also includes a circuit for normally exciting the phase windings Illa, 10b of the motor to develop a rotating magnetic field; specifically, the windings la and Nb may be conventional two-phase distributed windings connected to two-phase supply terminals I i.

The system of Fig. 1 also includes means for applying to the motor l0 an auxiliary sub-synchronous magnetic field to reduce the speed of the motor below synchronism. Specifically, this means may comprise means for applying to at least a portion of the winding system, for example, the auxiliary winding We, a controllable unidirectional current effective to develop a stationary magnetic field to control the speed of the motor. It will be understood that the winding Inc may be disposed in the same stator slots as the windings Illa and [0b and may be arranged to provide any desired number of pole pairs. The

aaeaoos system also includes means for varying the auxiliary winding current to control the speed of the motor. This means may comprise any source of direct current, such as a battery l2, and a voltage-divider resistor l3 connected thereacross and having an adjustable contact Ila. The winding We is connected across an adjustable portion of the voltage divider i3 through a choke coil ll to suppress the flow of alternating currents induced in the winding Me.

It is believed that the operation of the system of Fig. 1 will be apparent to those skilled in the art from the foregoing description. In brief, a periodic or alternating polyphase current is applied to the phi se windings iila, lob of the motor from the supply terminals II, which is effective to develop a rotating magnetic field in the motor causing it normally to run at synchronous speed. At the same time, an auxiliary unidirectional control current is applied to the auxiliary winding I from the voltage divider II! to control the speed of the motor. This auxiliary control current is effective to develop a sub-synchronous, specifically a stationary, magnetic field across the motor which reacts upon the hysteresis rotor illd to load or brake the same. The unidirectional current may be adjusted by adjustment of the contact l3a to such a value as to reduce the speed of the motor below synchronism but not to 'brake it to a stop. Under these conditions, ad-

justment of the control current by adjustment of the contact 13a is efiective to control or regulate the speed of the motor over a desired range of sub-synchronous speeds. On the other hand, if desired, the control current in the auxiliary winding l0c may be adjusted to a value sufiicient to reduce the speed of the motor rapidly to some predetermined sub-synchronous speed, for example, rapidly to brake the motor to a stop.

Thus, the motgr control system of Fig. 1 provides a motor,drive having the advantages of synchronous operation where desired and, in addition thereto, operation over a range of subsynchronous speeds which may be readily controlled merely by adjustment of the contact i311. Further, if desired. the contact I M may be adjusted rapidly to a point on the voltage divider I! such that the value of the auxiliary current in the winding I00 produces a powerful stationary magnetic field eflective to brake the motor rapidly to a stop. Such braking action may be effected with or without power applied to the motor windings Illa, lob, depending on the motor characteristics and the particular application involved.

Fig. 2 represents a modified form of the motor control system of the invention, in which the auxiliary winding i 00 is omitted and the winding system of the motor In comprises only the pair of two-phase windings Illa, lllb. The windings la and lob are energized from the single-phase supply circuit terminals IS, the winding Ina being connected directly to the terminals I 5 and the winding Nib being connected thereto through a phase-splitting condenser l6 for normally exciting the windings Illa, lllb in quadrature.

In the system of Fig. 2, the control circuit for developing the sub-synchronous auxiliary magnetic field is connected to apply to one portion of the winding system. specifically, to the phase winding lob. a unidirectional current effective to develop the desired stationary magnetic field. As in the system of Fig. 1, the winding I0!) is connected to be excited from a control circuit including a unidirectional source, such as a battery l2, and the voltage-divider resistor [3 having an adjustable contact "a. The system oi Fig. 2 includes impedance means for substantially suppressing the fiow of current in each of the supply circuits and the control circuit of the frequency of the other of said circuits. Specifically, the choke l4 suppresses the flow of alternating current from the supply terminals l5 through the control circuit including voltage divider i3 and source l2, while the phase-splitting condenser l6 also suppresses the flow of unidirectional current from the battery I! through the other phase winding Illa and the supply circuit is. The system of Fig. 2 is thus a simplification of that of Fig. 1, in which the auxiliary winding lllc of Fig. 1 may be omitted. However, the magnetic circuit including the winding iOb of Fig. 2 must be designed so that it does not become saturated by the combined exciting current and control current during normal operation. In other respects, the operation of the system of Fig. 2 is similar to that of Fig. 1. The value of the auxiliary unidirectional current through the winding IOb may be adjusted either for continuous regulation or control at sub-synchronous speeds or to brake the motor rapidly to a stop. The circuit arrangement of Fig. 2 may also be applied to a polyphase motor in which case the condenser It serves only as a direct-current blocking condenser and preferably has a value sufliciently large that it does not cause a substantial phase shift of the supply current.

In Fig. 3 there is represented a further modifled motor control system embodying the invention, in which the control circuit for applying to a portion of the motor winding system a current effective to develop a sub-synchronous magnetic field is responsive to a variable source of control signal for varying the control current to control the speed of the motor. The motor III of Fig. 3 is represented as of the two-phase type having phase windings Illa, illb electrically insulated from each other. The windings inc and lb are supplied from the four-phase supply terminals Ila, ilb, the latter being energized through an insulating transformer [8. In the case of a conventional three-wire two-phase supply circuit, the lower terminal Fla and the upper terminal ilb may be connected together. In this system, the auxiliary control current is applied to the phase winding lllb from a control circuit including a source, such as a battery l2, a choke II for suppressing the flow of alternating current, a resistor l9, and a vacuum tube 20 which, for simplification, is shown as a triode, but which may be any suitable type of repeater or amplifier having a unidirectional output. The grid of the tube 20 is excited from any suitable source of control signal 2i and is returned to its cathode through a grid leak 22 and a negative bias battery 23. It will be understood that the control signal developed by the unit 2| may be in response to variations of any controlling quantity, for example, temperature, pressure, speed, etc.

The operation of the system of Fig. 3 is in all respects similar to that of the systems of Figs. 1 and 2. Variations in the control signal 2i control the repeater tube 20 to vary the unidirectional control current applied to the winding lob which develops the auxiliary stationary magnetic field for control purposes. The insulating transformer I8 suppresses the flow of unidirectional current through the supply circuit connected to the terminals I'Ib, while the choke i4 suppresses the flow of alternating current through the source II.

In Fig. 4 there is represented a simplified form of the system of Fig. 3 in which the motor is of the single-phase type utilizing a phase-splitting condenser as in the system of Fig. 2. However. in the circuit of Fig. 4 the tube 2| comprises a self-rectifying control device so that it eflectively constitutes a unidirectionally controllable impedance across the winding llb to control the unidirectional component of current therein. The principles of operation of the system of Fig. 4 are similar to those of the system of Fig. 3, described above. The circuit of Fig. 4 has the advantage that the energy-dissipating resistor i and the choke coil 14 may be eliminated.

In Fig. 5 there is represented a motor control system embodying the invention and including means responsive to an electrical characteristic of the motor excitation, such as the current to. or the voltage across. the motor windings for controlling the auxiliary magnetic fleld. In the system of Fig. 5 there is represented a threephase hysteresis motor 24 having the three-phase windings 24a, 24b, and Mo connected to the three-phase supply circuit terminals 25 through a disconnect switch 26 of any conventional wellknown type. The system is also provided with a control circuit including a source of unidirectional current, such as the battery It. for applying to at least a portion of the winding system of the motor, for example, the winding b. a current effective to develop a subsynchronous magnetic held, as described above.

The system of Fig. 5 also includes relay means responsive to interruption of excitation of the motor, either voltage or current, for closing the control circuit for activating the field-applying means. For example, the relay means may be a current relay 21 having a winding 21a included in series in one of the supply circuit connections. a core' 21b, and an armature 21c carrying the movable one of a pair of contacts lid. The armature 210 is biased into circuit closing position by means of a spl'ing Us.

In the operation of the system of Fig. 5, when current is supplied to the motor so that it is operating normally. the winding 21a of relay i1 is energized to hold open the contacts 21d and the motor 24 operates as a conventional synchronous 6 directional current to the winding b from the battery I! of a value sufllcient to brake the motor rapidly to a stop.

- While there have been described what are at present considered to be the preferred embodi- I ments of the invention. it will be obvious to those skilled in the art that various changes and modiiications may be made therein without departing mm the invention. and it is. therefore. aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is: v l. A motor control system comprising: a synchronous hysteresis motor having a plurality of phase windings and a hysteresis rotor. a circuit for normally exciting said windings. to develop a rotating magnetic field, a control circuit for api li' s to at least one of said phase windings a current eiiective to develop a sub-synchronous magnetic held of a value to reduce the speed of the motor below synchronism, and impedance means for substantially suppressing the flow of current in each of said circuits oijthe frequency oi'the other of said circuits.

{2. A motor control system comprising: a synchronous hysteresis motor havingfa' plurality of phase windings and a hysteresis rotor. a singlephase supply circuit including a phase-splitting condenser for normally exciting said windings to develop a rotating magnetic field, a control circuit for applying to one of said windings a unidirectional current eifective to develop a statfioInary magnetic field of a value to reduce the speed of the motor below synchronism, said condenser serving to suppress the flow-of unidirectional current in said supply circuit and a choke coil for suppressing the flow of current from said supply circuit in said control circuit. HERBERT C. ROTERS.

nnrnasncas crrnn -The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Parvin Mar. 12, 1940 Snyder Apr. 9, 1940 sweeny July so, 1940 Rotors Sept. 7, 1943 Number 

